Some recalculations, now I can see MDWS directly...
The distances are, I reckon, nearer 750m to the cabinet (assuming 0.5mm copper), with the cab 4km from the exchange.
The "gap" in bit-loading (in the bits/tone) is slightly larger than I originally remembered, but it is still perhaps a third of the size of mine. I reckon that still gives you a 5-6Mbps advantage over lines with cabs about 2km away.
If we compare you with other lines in the 48Mbps region, as seen on MDWS:
- You appear to be have almost identical physical properties (the line attenuation values) to "Kamix2" and "digginsa"
- You appear to have very similar patterns of bit-loading to these two lines
- But you're a little different to "Ronski", whose line appears to have lower attenuation. That line gets better performance out of U2 and D3 than yours, but comparatively worse performance in U1 (fewer bit/tone) and D1 (a bigger hole caused by the ADSL power masks).
One thing to add. My line characteristics are a bit odd. My line length for the above speeds is somewhere around 1.3km which would never give speed reading anywhere near that in normal circumstances!
I still can't figure this last sentence out. Are you saying that your line is actually 1.3km? Or that the line characteristics suggest it is 1.3km? Or that the speeds suggest it is 1.3km?
The attenuation tells you what a line is behaving like electrically, and is often converted into a distance for convenience - using the scale factor for 0.5mm copper. However, just remember that the attenuation actually depends on the material (copper vs aluminium), the length, and the gauge or diameter ... and the gauge has a significant impact.
This BT-Cables page shows CW1128-spec copper cables of 4 different gauges: 0.5mm, 0.6mm, 0.63mm and 0.9mm, while the PDF includes 0.4mm too (which I think is used on my line).
The resistance plays a significant role in the attenuation - and the following lines would all have the same resistance:
- 480m of 0.4mm copper
- 750m of 0.5mm copper
- 1.1km of 0.6mm copper
- 1.2km of 0.63mm copper
- 2.4km of 0.9mm copper
All five lines would behave in a similar manner.
In general, duct space becomes the critical factor nearer the exchange, and thin copper can be used to save space. Out in the country, keeping within the maximum resistance becomes the critical factor for long lines, and fat copper has been used in the past to offset the extended distance - so that the line stayed within the limits needed for a voice service. Over the whole length of a line between premises and exchange, the gauge can change.
